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Experiments in a central California Macrocystis pyrifera (L.) C.A. Agardh forest examined the effects of long-term (six year) kelp canopy exclusion on the abundance of the annual brown alga Desmarestia ligulata (Light F). Exclusion of both surface and subsurface kelp canopies from replicate clearings within stillwater Cove, CA, USA showed that D. ligulata sporophyte recruitment is opportunistic, with more sporophytes occurring in areas where canopies were excluded than under control canopies. Kelp canopy exclusion also increased spring and summer bottom irradiances, and resulted in a steady increase of perennial turf algae over the six-year study. This, in turn, led to a decrease in the availability of nongeniculate coralline algae (the primary substratum on which D. ligulata recruits). Subsequently, the annual maximum abundance of D. ligulata sporophytes decreased in the Canopy clearings, but did not change under control canopies. Removal of turf algae from experimental plots further increased bottom irradiances and significantly enhanced D. ligulata recruitment. When released from apparent competition for light and space, D. ligulata sporophytes exhibited an annual life history, with recruitment occurring during a two-week period (April 4- April 17) in the spring, and maximum bottom cover occurring in the summer (July). The onset of Desmarestia sporophyte recruitment was closely associated with seasonal increases in daylength and rapid decreases in ocean temperature. These results indicate that the Desmarestia sporophyte life history is both annual and opportunistic, with the onset of recruitment stimulated by predictable, seasonal changes in environmental conditions, and the magnitude of recruitment modified by stochastic processes that affect the availability of light and space. Comparison of these results with those from similar studies indicate that they are robust and suggest that they may be generalized over broad temporal and spatial scales., Cited By (since 1996):43, Seaweeds, CODEN: JEMBA, ,

The deep-water macroalgal assemblage was described at 14 sites off the central California coast during 1999 and 2000 from SCUBA and remotely operated vehicle sampling. The stipitate kelp Pleurophycus gardneri Setchell & Gardner, previously thought to be rare in the region, was abundant from 30 to 45 m, forming kelp beds below the well-known giant kelp forests. Macroalgae typically formed three broadly overlapping zones usually characterized by one or a few visually dominant taxa: 1) the upper "Pleurophycus zone" (30-45 m) of stipitate kelps and Desmarestia spp. with a high percent cover of corallines, low cover of uncalcified red algae, and rare green algae; 2) a middle "Maripelta zone" (40-55 m) with other uncalcified red algae and infrequent corallines and green algae; and 3) a zone (55-75 m) of infrequent patches of non-geniculate coralline algae. The green alga Palmophyllum umbracola Nelson & Ryan, not previously reported from the Northeast Pacific, was found over the entire geographical range sampled from 35 to 54 m. Year-round profiles of water column irradiance revealed unexpectedly clear water with an average K0 of 0.106·m-1. The low percent surface irradiance found at the average lower macroalgal depth limits in this study (0.56% for brown algae, 0.12% for uncalcified red algae, and 0.01% for nongenictilate coralline algae) and lack of large grazers suggest that light controls the lower distributional limits. The ubiquitous distribution, perennial nature, and similar lower depth limits of deep-water macroalgal assemblages at all sites suggest that these assemblages are a common persistent part of the benthic biota in this region., Cited By (since 1996):26
Seaweeds, CODEN: JPYLA, ,

Using in situ substratum sterilization and fluorescence microscopy in studies of microscopic stages of marine macroalgae,

Description

The methods currently used for examining the relative contribution of microscopic stages to the persistence of natural populations of marine macroalgae can be inappropriate for use in subtidal habitats. Also, because of their microscopic size, direct examination and obtaining an estimate of recruitment, growth and mortality of these stages in the field is difficult. A method of removing microscopic algal stages from natural rock surfaces using watertight tents and water-soluble chemicals is presented. Also discussed is the use of a previously described method of fluorescent labelling these microscopic stages that, when examined under UV light, allows for their precise identification and growth to be determined. Together, these methods can be effective in examining the ecology of algal microscopic stages in the field., Cited By (since 1996):1, Seaweeds, CODEN: HYDRB, ,

Delayed recruitment of microscopic stages in respouse to cyclical cues is critical to the population dynamics of many annual and seasonally reproducing perennial seaweeds. Microscopic stages may play a similar role in continuously reproducing perennials in which adult sporophytes are subject to episodic mortality, if they can respond directly to the unpredictable onset and relaxation of unfavorable conditions. We experimentally evaluated the potential for temporary reduction in limiting resources (light, nutrients) to directly delay recruitment of giant kelp (Macrocystis pyrifera (L.) C.A. Agardh) gametophytes and embryonic sporophytes. Laboratory cultures were subjected to limiting conditions of light and nutrients for 1 month and then exposed to non-limiting conditions for 10 days. Gametophytes in all treatments failed to recruit to sporophytes after 2 weeks, suggesting they are not a source of delayed recruitment in giant kelp. Sporophytes in light-limited treatments, however, survived and grew significantly slower than non-light-limited controls. When stimulated with light, light-limited sporophytes grew from 2 to >10 times faster than unstimulated controls depending on nutrient availability. These results suggest that limiting resources can delay recruitment of embryonic giant kelp sporophytes for at least 1 month. Flexible timing of recruitment from embryonic sporophytes may enhance persistence of continuously reproducing perennial species when macroscopic adults are subject to episodic large-scale removals., Cited By (since 1996):24,
Seaweeds, CODEN: JPYLA

Coupling propagule output to supply at the edge and interior of a giant kelp forest

Description

Propagule dispersal is fundamental in regulating the strength of demographic and genetic interactions between individuals both within and among populations. I studied spatiotemporal variability in propagule (zoospore) supply of a continuously reproducing seaweed, giant kelp Macrocystis pyrifera, to examine: (1) the extent to which local zoospore production is coupled to (correlated with) temporal variability in zoospore supply; and (2) spatial variability in the strength of such coupling. Macrocystis pyrifera planktonic zoospores were quantified from seawater samples pumped on numerous dates in 1999 from just above the substratum at various sites in the Point Loma kelp forest, southern California, USA. Zoospore collections were made at a site in the forest interior approximately three times per month from late February through mid-November. Sample collection overlapped with complete demographic surveys of the local population (100 m2) to determine local reproductive output. Temporal variability in zoospore supply was strongly correlated with relative changes in the density .and size structure of local reproductive adult sporophytes; 76% of variability in zoospore supply was explained by local reproductive output. This tight coupling between zoospore supply and local reproduction appeared to be driven by low-displacement, oscillating currents in the forest interior due to the cumulative drag of adult sporophytes, which kept zoospores close to their release site. High coupling between zoospore supply and local reproduction was validated at two additional interior sites separated by 1 km; 78% of variability in zoospore supply was explained by local reproductive output at these sites. Due to lower sporophyte densities, however, the forest edges experienced rapid, unidirectional currents that appeared to transport zoospores far from their release site, effectively decoupling zoospore supply from local reproduction; only 38% of variability in zoospore supply was explained by local reproductive output at these sites. The results suggest that the size of and location within kelp populations is an important determinant of the importance of local reproduction to zoospore supply due to the effects of flow modification by kelp canopies on zoospore dispersal., Cited By (since 1996):27
Seaweeds, CODEN: ECOLA

A biooptical model of irradiance distribution and photosynthesis in seagrass canopies,

Description

Although extremely vulnerable to coastal eutrophication, seagrasses represent important structuring elements and sources of primary production in shallow waters. They also generate an optical signature that can be tracked remotely. Accurate knowledge of light absorption and scattering by submerged plant canopies permits the calculation of important plant- and ecosystem-level properties, including rates of photosynthesis, vegetation abundance, and distribution. The objectives of this study were to develop a realistic, yet simply parameterized two-flow model of plane irradiance distribution through a seagrass canopy submerged in an optically active water column, to evaluate its performance against in situ measurements, and to explore the impacts of variations in canopy architecture on irradiance distribution and photosynthesis within the canopy. Allometric functions derived from leaf length-frequency data enabled simple parameterization of canopy architecture. Model predictions of downwelling spectral irradiance distributions in seagrass canopies growing in both oligotrophic and eutrophic waters were within 15% of field measurements. Thus, the model provides a robust tool for investigating photosynthetic performance of seagrass canopies as functions of water quality, depth distribution, canopy architecture, and leaf orientation. Model predictions of upwelling irradiance were less reliable, particularly in the upper half of the canopies. The model was more sensitive to leaf orientation than leaf optical properties, seabed reflectance, or the average cosine of downwelling irradiance. Better knowledge of leaf orientation appears to be a fruitful avenue for improving our understanding of the interaction between seagrasses and the submarine light environment., Cited By (since 1996):36, Seaweeds, CODEN: LIOCA, ,

Effect of high irradiance on recruitment of the giant kelp Macrocystis (Phaeophyta) in shallow water

Description

Laboratory and field experiments were done in Stillwater Cove, Carmel Bay, California, and Monterey Harbor, California, to determine the effect of photosynthetically active radiation (PAR) on the shallow (upper) limit of giant kelp, Macrocystis pyrifera (L.) C. Agardh. At shallow, depths, M. pyrifera did not recruit or grow to macroscopic size from gametophytes or embryonic sporophytes transplanted to vertical buoy lines; sharp decreases in PAR with depth coincided with observed recruitment and sporophyte distributions. Shade manipulations indicated that settlement of M. pyrifera zoospores was decreased, but not prohibited, by high PAR. Postsettlement stages (gametophytes and embryonic sporophytes), however, survived only under shade. These results suggest that high PAR can inhibit the recruitment of M. pyrifera to shallow water by killing its postsettlement stages; whether or not ultraviolet (UV) radiation also inhibits recruitment was not tested. In either case, however, it appears that high irradiance (PAR and/or UV) regulates the shallow limit of M. pyrifera prior to temperature and desiccation stresses inherent to intertidal regions. In an additional experiment, recruitment or growth of transplanted gametophytes or embryonic sporophytes of Macrocystis integrifolia Bory also did not occur at shallow, depths, suggesting that this shallow water species accesses high irradiance regions via a method other than sexual reproduction., Cited By (since 1996):31, Seaweeds, CODEN: JPYLA

Taxonomic reassessment of rhodolith-forming species of Lithophyllum (Corallinales, Rhodophyta) in the Gulf of California, Mexico,

Description

Rhodolith beds (beds composed of unattached coralline red algae) in the Gulf of California, Mexico, are widespread and commonly dominated by specimens belonging to Lithophyllum. The number of rhodolith-forming species of Lithophyllum in these beds, however, has been uncertain, and there are contradictory statements in the recent literature concerning putative species. Five species have been recognized, but it also has been suggested that these represent only a single polymorphic species. More than 700 specimens from 45 localities were examined and compared with all relevant types to determine how many species are represented and how they might be distinguished. Most of the types analyzed agree with the modern concept of Lithophyllum; however, two species, Lithophyllum californiense Heydrich and Lithophyllum bracchiatum (Heydrich) Me. Lemoine, do not agree with the modern concept of Lithophyllum and have been excluded from the genus. None of the characters used previously to delimit species in the group was taxonomically reliable. Moreover, an evaluation of all specimens based on modern characters, especially relating to tetrasporangial conceptacle anatomy, showed that only a single species was present, namely Lithophyllum margaritae (Hariot) Heydrich. Both within and between populations, L. margaritae exhibits a continuum of growth forms: encrusting to foliose to fruticose to warty to lumpy. The dominance of particular growth forms within an area appears to be linked to local environmental conditions., Cited By (since 1996):41, Seaweeds, CODEN: PYCOA, ,

The role of alternate life-history stages of a marine macroalga: A seed bank analogue?,

Description

Many organisms occurring in temporally variable environments have evolved life-history traits that enable their populations to persist during unfavorable environmental conditions. Numerous terrestrial plants, insects, and marine invertebrates, for example, rely on resting stages that disperse their propagules in time. Although widely observed among many taxa, few examples exist for marine macroalgae, at least in part because of the methodology involved in studying them. Here, I determined that microscopic life stages of the annual marine macroalga Desmarestia ligulata overwinter during periods when the macroscopic thalli are absent, thereby allowing this species to persist in temporally variable environments. Examination of field-grown microscopic stages with fluorescence microscopy identified these stages as gametophytes. Holdfast tagging experiments determined that recruitment of the macroscopic stages was not enhanced by regrowth of perennial thalli as observed in other macroalgae, suggesting that overwintering gametophytes were the sole source of sporophyte recruitment. In contrast to true resting stages, Desmarestia gametophytes were not dormant, but rather were metabolically active, sensitive to small differences in environmental quality, and highly subject to physical damage. Gametophyte photosynthetic rates were greater under higher irradiance, and growth rates were greater under longer photoperiods and higher irradiance. Although their survival appeared to be reduced by grazing from large (>1 cm) invertebrates and sedimentation, gametophytes were able to survive in the field for at least 15 mo and thereby enhance sporophyte recruitment more than a year after settlement. I suggest that Desmarestia gametophytes be regarded as alternate life-history stages that simply maintain populations under a different set of environmental conditions than the macroscopic sporophytes do, rather than as 'dormant' or 'resting' stages., Cited By (since 1996):25, Seaweeds, CODEN: ECOLA, ,

Cytometric quantification of nitrate reductase by immunolabeling in the marine diatom Skeletonema costatum,

Description

Background: The uptake of nitrate by phytoplankton is a central issue in biological oceanography due to its importance to primary production and vertical flux of biogenic carbon. Nitrate reductase catalyzes the first step of nitrate assimilation, the reduction of NO'3 to NO 2. A cytometric protocol to detect and quantify relative changes in nitrate reductase (NR) protein content of the marine centric diatom Skeletonema costatum is presented. Methods: Immunolabeling of NR protein was achieved with polyclonal antibodies raised against S. costatum NR. Antisera specific to a NR protein subunit and to a NR polypeptide sequence were compared and cytometric results of NR protein abundance were related to Western analyses. Changes in cellular NR abundance and activity were followed during an upwelling simulation experiment in which S. costatum was exposed to a shift from ammonia to nitrate as major nitrogen source. Results: NR protein could be detected in NO 3-grown cells and at extremely low levels hardly discernible by Western Blot densiometry in NH 4-grown cells. The protocol allowed observation of early stages of NR induction during an upwelling simulation. NR abundance increased after the nutrient shift to reach a new physiological 'steady- state' 96 hrs later. NR activity exhibited diel variation with maxima at mid- day. NR abundance as estimated by both flow cytometry and Western analysis exhibited a hyperbolic relationship to NR activity. This pattern suggests post-translational activation of NR protein. Conclusions: The presented protocol allows the differentiation of NH 4- versus NO 3-grown algae as well as the monitoring of early stages in the induction of nitrate assimilatory capacities. (C) 2000 Wiley-Liss, Inc., Cited By (since 1996):8
Seaweeds, CODEN: CYTOD, ,

Seed bank, biomass, and productivity of Halophila decipiens, a deep water seagrass on the west Florida continental shelf,

Description

One of the largest contiguous seagrass ecosystems in the world is located on the shallow continental shelf adjacent to the west coast of Florida, USA and is comprised of seasonally ephemeral Halophila decipiens meadows. Little is known about the demography of the west Florida shelf H. decipiens, which may produce 4.56 × 108 g C day-1 or more during the peak growing season. We documented seagrass distribution, biomass, and productivity, and density of sediment seed reserves, seedlings, flowers and fruits on the southeastern portion of the west Florida shelf by sampling along a transect at three stations in 10, 15, and 20 m water depth. Biomass, flower, fruit, seedling, and seed bank densities tended to be highest at stations in 10-15 m water depth and lowest at 20 m. Flowers and fruit were most prevalent during summer cruises (June and August 1999, July 2000). Seedling germination occurred during summer, fall (October 1999), and winter (January 2000) sampling events, with the highest seedling densities present during the winter. Seed bank density remained consistent through time. A Category I hurricane with sustained winds of 120 km h-1 passed over the stations, but only limited impact on H. decipiens biomass was observed. The presence of a persistent seed bank provides for recovery after storm disturbance, annual reestablishment of populations, and continual maintenance of the 20,000 km2 of deep water seagrass habitat present on the west Florida shelf., Cited By (since 1996):15, Seaweeds, CODEN: AQBOD, ,

Control of community growth and export production by upwelled iron in the equatorial Pacific Ocean

Description

The iron hypothesis states that phytoplankton growth and biomass are limited by low concentrations of available iron in large regions of the world's oceans where other plant nutrients are abundant. Such limitation has been demonstrated by experiments in which iron has been added to both enclosed and in situ (un-enclosed) phytoplankton populations. A corollary of the iron hypothesis is that most 'new' iron is supplied by atmospheric deposition, and it has been suggested that changes in the deposition rates of iron-bearing dust have led to changes in biological productivity and, consequently, global climate. Here we report surface-water measurements in the equatorial Pacific Ocean which show that the main iron source to equatorial waters at 140°W is from upwelling waters. Shipboard in vitro experiments indicate that sub-nanomolar increases in iron concentrations can cause substantial increases in carbon export to deeper waters in this region. These findings demonstrate that equatorial biological production is controlled not solely by atmospheric iron deposition, but also by processes which influence the rate of upwelling and the iron concentration in upwelled water., Cited By (since 1996):221
Seaweeds, CODEN: NATUA

One of the most commonly predicted effects of global ocean warming on marine communities is a poleward shift in the distributional boundaries of species with an associated replacement of cold-water species by warm-water species. However, these types of predictions are imprecise and based largely on broad correlations in uncontrolled studies that examine changes in the distribution or abundances of species in relation to seawater temperature. Our study used an 18-year sampling program in intertidal and subtidal habitats and before-after, control-impact analyses. We show that a 3.5°C rise in seawater temperature, induced by the thermal outfall of a power-generating station, over 10 years along 2 km of rocky coastline in California resulted in significant community-wide changes in 150 species of algae and invertebrates relative to adjacent control areas experiencing natural temperatures. Contrary to predictions based on current biogeographic models, there was no trend toward warmer-water species with southern geographic affinities replacing colder-water species with northern affinities. Instead, the communities were greatly altered in apparently cascading responses to changes in abundance of several key taxa, particularly habitat-forming subtidal kelps and intertidal foliose red algae. Many temperature-sensitive algae decreased greatly in abundance, whereas many invertebrate grazers increased. The responses of these benthic communities to ocean warming were mostly unpredicted and strongly coupled to direct effects of temperature on key taxa and indirect effects operating through ecological interactions., Cited By (since 1996):91, Seaweeds, CODEN: ECOLA, ,